Morphological Characteristics And Oxbow Lake Evolution Of Meandering Rivers In The Yellow River Source Region

In order to obtain the morphological characteristics of the meandering river and the evolution law of the cow oxbow lake,using the analysis of remote sensing image,field investigation and mathematical model,three kinds of methods are discussed,according to the spatial scale from large to small(river group-river-oxbow lakes),the bend-belt and the neck-mouth cutting-bending ratio,the channel type and geological characteristics,the classification of oxbow lakes and the formation process of sand suppository have provided reference information for the study of meandering river and oxbow lakes.There are a lot of meandering rivers in the source of the Yellow River,mainly forming three meandering river groups in Zoige,Gannan and Huangnan.The meandering belt is inversely proportional to the slope gradient,and the number of bovine yoke lakes is positively related to the mean curvature of the river,negatively related to the slope gradient of the river,and the percentage of neck cut ratio with meadows is increasing.In the 3 curved river groups,the neck-mouth meandering ratio increased first and then decreased and then increased,and the alluvial part of Zoige was generally less than 0.3;the decrease of precipitation along the Yellow River is the main reason for the decrease of meadow and shrub growth.The terrain condition makes the curved river develop the unrestricted,restrictive,semi restrictive three kinds of rivers.In May 2017,the field survey of hot blasts showed that non-restricted rivers are generally continuous curved roads with little geological changes on both banks.The peat layer is 0.95?1.03 m,and the clay layer is 0.63?0.92 m;the clay layer of the restrictive channel is the thickest.There are five groups of soil samples exceeding 1 m,and the thickness of the clay layer increases by 0.55 m from the bank to the foot of the mountain at a distance of 62 m,with the greatest rate of change.The semi-restricted rivers have the fastest rate of bending,the largest degree of curvature,and they are concentrated at 2.07 to 2.81.There are large and limited angles in the restrictive rivers,and the angular variance is generally high,concentrating on 900?4200.2016?2017 Hei River field visit,the width of the bend belt along the Hei River from upstream to downstream is increased,the trend of change in the growth rate is "urgent-slow-urgent",in the middle of the cattle oxbow lake number.The oxbow lake in the lower reaches of the Hei River is more affected by siltation.It takes much less time to develop from the ?-type yoke lake to the U-shaped and C-shaped than to the upper and middle reaches of the oxbow lake.By constructing the deposition model of the inlet section of the oxbow lake,we know that the shorter the sand plug,the larger the upstream sediment volume,and the larger the diversion angle,the shorter the time required for the deposition of the bull yoke lake inlet to complete.The error of the new original channel depth,the sand bolt height and the measured value is 11%,the actual siltation shape of the inlet section is ladder type.Using Mike Zero to simulate the water and sediment in the outlet section of the cattle oxbow lake,the plane can find the vortex in the direction of the cow oxbow lake,and the longitudinal profile can be found near the downstream section for the flow into the oxbow lake direction.The finer the median particle size of incoming sand,the faster the sedimentation rate at the outlet of the oxbow lake,but the deposition of the cross-section is random.The larger the upstream flow,the faster the sedimentation velocity of the oxbow lake outlet,and the difference in flow between the river center and the river channel.When the flow rate increases,the river banks will sink faster than the center of the river channel.When the upstream sediment concentration is greater,the sedimentation rate at the outlet of the oxbow lake is faster and the overall impact is even.